Inside a Bell & Howell Eyemo

Among wind-up cameras Bell & Howell's 35mm Eyemo (and its 16mm brother the Filmo) stand apart, as products of the highest technical standards. Their simple but precise mechanism, and extremely durable construction made them quickly popular among newsmen and military photographers, who used them to cover everything from the Spanish Civil War right through to Vietnam. In the movie industry Eyemos were often used as "crash cams", where their low cost, stable images and indestructability proved highly valuable for dangerous stunt work.

The Eyemo was first released in 1925, as a single lens 100 foot spool load model, based very much on the 16mm Filmo that had come out a year or so earlier. Despite the quality of its construction, it was intended to serve the amateur or semi-professional market. Later models came with triple lens turrets and viewfinders with their own matching lens turret. The model Q pictured, also nick-named "spyder", had the lenses spaced out to avoid a neighbouring lens hood sticking in to the frame, and came with an additional critical viewfinder and the ability to take magazines. The internal mechanics however remained virtually unchanged since the first model.

A few different Eyemos, including a PL mount "crash cam" front and centre.                                                                                                                                                                                                                          

Because they use an uncased spring, dismantling Eyemos and Filmos can be very dangerous if you don't know what you're doing. The force unleashed by a coiled length of spring steel can be tremendous, even when they have been run right down, and the edges are very sharp. For this reason I would advise inexperienced people not to attempt to completely dismantle one of these cameras. 

With certain precautions it is safe to remove the front housing and access the shutter and intermittent mechanism. Many times this will be the area that is causing a camera to stop running.

Once the turret has been removed, 2 screws on either side of the front plate and one inside the film chamber above the gate can be undone and the whole front mechanism comes out. A stop pawl in the front (activated by the release lever protruding through from the camera side at the bottom of the cavity pictured) is all that is keeping the camera from running, so if the spring is wound at all (and the jam is indeed in the front mechanism), it will start running the moment the front is removed.

So to be safe, before removing anything the spring should be run down as far as it will go. A 13 tooth idler gear visible through a hole in the film chamber controls the duration of the run (the left gear in the picture). It runs directly off a 14 tooth gear connected to the spring shaft, and after 12 revolutions a shallow valley on the main gear hits a long tooth on the idler gear and locks. To completely wind down the spring, the idler gear can be depressed with a screwdriver to allow the spring to keep turning until there is no driving force left. 

If the camera is jammed (as is often the case when a service is required) the spring cannot be run down, so it may fire up when the front is removed. In this case I set the speed to the lowest setting.

The front plate houses the shutter, stop pawl, intermittent mechanism and gate. When removing the gate be careful to note the spring beneath the side rail (at the top of the picture) that applies pressure to the side of the film and controls lateral steadiness.

The pulldown mechanism is a marvel of simple yet effective design. The cam should spin quite freely when the stop pawl (on the left in the picture) is activated. I lightly grease the cam surface, follower, shuttle and shuttle pins. The shutter bearing can be oiled from the other side.

Often the shutter needs some straightening to avoid scraping. To prevent excessive vibration it is made of very lightweight but easily deformed tin plate. 

According to the service manual, any further dismantling requires the spring to be fully wound 

up (with the front fitted) and then run at the lowest speed until the long tooth of the idler gear is visible. It should then be depressed and the camera run again until the shallow valley of the main gear is visible, at which point the two gears can be locked together to prevent any further unwinding. Now the front can come off, the 4 smaller screws around the edge of the top mechanism plate can be undone and the entire mechanism, tightly wound spring and all, can be carefully removed. At this point a special jig to hold the spring needs to be fitted so that it can be detached from the rest of the mechanism. Without a jig do NOT attempt this procedure!

I don't have a jig, and don't really like the idea of removing the spring fully wound, so I take a different tack. With the spring completely wound down (the idler gear must be depressed as described earlier) I remove the curved strip connecting the speed selector to the governor, and the 2 sprockets. Then I remove all of the screws - the 4 smaller ones holding the mechanism into the body, the 6 (or sometimes 5) larger ones holding the two mechanism plates together, and the 'special' screw (with 2 holes rather than a slot) next to the feed spindle that controls the feed tension. If there is any spring tension remaining,  separating the top plate from the bottom plate will cause gears to slip and the spring to suddenly unwind at full speed. It makes a terrifying sound, and will strip the teeth from gears. So you can't do this if the mechanism is jammed and the spring not fully unwound.




With some careful jiggling the top mechanism plate can be separated from the bottom plate. The bottom plate is loose but still connected to the spring beneath, so it needs to remain in place or it will lift the spring out with potentially nasty consequences.
On the underside of the top plate you can see the rather compact speed governor with its gearing, the feed and take-up spindle clutches and the two pawls attached to an eccentric shaft which drive the footage counter ratchet.




A close-up of the top mechanism plate with some of the gears removed. At left, the take-up clutch with its gear, at right the feed clutch. Just off centre you can see the idler gear that limits the spring wind in both directions, mounted with a small spring that allows it to be depressed from the film chamber. At the top is the speed governor - a worm gear driven shaft with arms that expand out with centrifugal force, housed within a sliding case that limits how far the arms can extend. The oil holes in the film chamber lubricate the governor - its two bearings, the sliding casing, and the worm drive gear.





The bottom mechanism plate. In the centre are the large main drive gear and (connected to the same shaft) the smaller gear with one shallow valley that meshes with the limit idler. Underneath, the shaft hooks into one end of the motor spring. By rotating the shaft anti-clockwise it will unhook from the spring and allow the bottom plate to be removed.







The motor spring revealed. The outer end (at top right) is held in place by a long pin that extends up through both mechanism plates. The spring is lubricated with graphite powder.
Reassembling everything in situ can be a little tricky. Certain gears need to be fitted to either one or the other mechanism plate. It usually takes me several tries to eventually get everything together with all the bearing shafts properly located. Before assembly, every bearing is lubricated with a drop of oil.


To reset the idler gear, the spring is wound several revolutions with the idler depressed before allowing it to re-engage. It should stop the spring from being wound before the point where it becomes very tight, and stop it unwinding before it slows down excessively. It often takes a few goes to get the meshing right.